In HTML, the doctype is the required "<!DOCTYPE html>" preamble found at the top of all documents. Its sole purpose is to prevent a browser from switching into so-called "quirks mode" when rendering a document; that is, the "<!DOCTYPE html>" doctype ensures that the browser makes a best-effort attempt at following the relevant specifications, rather than using a different rendering mode that is incompatible with some specifications.
Definition and Usage
All HTML documents must start with a
The declaration is not an HTML tag. It is an "information" to the browser about what document type to expect.
In HTML5, the
<!DOCTYPE> declaration is simple:
In older documents (HTML 4 or XHTML), the declaration is more complicated because the declaration must refer to a DTD (Document Type Definition).
<!DOCTYPE html> <html> <head> <title>Title of the document</title> </head> <body> The content of the document...... </body> </html>